The present invention can be applied, for example, to cellulose and the demand of the papermaking industry to form webs of fiber suspensions, which often exceed 10 meters in width, and which are required to meet very high requirements on uniformity, both in the transverse and longitudinal directions. Indeed, the uniformity of these webs is often of decisive importance in terms of the efficiency and economy of the process.
During the liquid treatment of fiber suspensions, for example, such as during their washing or bleaching and dewatering, it is essential that the pulp is supplied to and transversely distributed on a running liquid-permeable support as uniformly as possible, both in the transverse and longitudinal directions. It is also essential that the processing liquid be distributed uniformly across the pulp web. Such uniform distribution prevents channelization, and thus uneven liquid treatment and dewatering.
In order to make optimum usage of the apparatus being employed, a suspension of cellulose fibers to be dewatered, such as in connection with a liquid treatment, must be supplied at the highest possible concentration and formed on the support, through which liquid is sucked out. This support can be a perforated roll or a planar wire. The desired highest possible concentration is controlled by the capacity of the equipment to transversely distribute the medium with sufficient uniformity and to form a homogeneous web in order to satisfy the demand of the process in question. The difficulty of distributing the fiber suspension uniformly across the entire width increases rapidly with increasing pulp concentration, due to the increasing shearing strength of the fiber network.
A non-uniform distribution of the fiber suspension not only results in non-uniform dewatering, and thereby yields a poor efficiency of the liquid treatment, but it can also cause damage to the fibers in a press, and thereby deteriorate the pulp quality. In the nip between the rolls, for example in a press, fiber flocks and thick portions of the pulp web can be subjected to such high pressure forces that the fibers are damaged in these load-carrying portions.
It is therefore apparent that a uniform distribution of the fiber suspension as well as of the processing liquid is of utmost importance for both the quality of the final product and of the economy of the process. Many different distribution devices have been developed in attempts to solve the aforesaid problems, but in many cases the problems remain, especially during sheet forming at high fiber concentrations.